Astrophysical Phenomena Research Articles

Features of anisotropic compact stars in rastall teleparallel gravity via linear equation of state

This paper aims to discuss the model of compact stars based on spherically symmetric spacetime, with a focus on the gravitational effects of Rastall teleparallel gravity, where T represents torsion and λ represents the Rastall parameter. In this study, we evaluate the spherically symmetric spacetime component e a(r) in terms of e b(r) using the linear equation of state p r = β ρ + γ, while the other component e b(r) is assumed from the literature. The paper delves into a detailed analysis of various properties of compact stars such as energy density profile, pressure components, gradients profiles, anisotropic conduct, energy limits, equation of state profiles, velocities of sound profiles, TOV equation profiles, and compactification profile. We use the well-known junction conditions to facilitate the evaluation of the unknown parameters, taking the standard Schwarzschild metric as the outer spacetime. Through detailed analysis in graphical form, we demonstrate that the model showing the anisotropic conduct of stellar objects is viably legitimate, regular, and stable. Overall, the paper provides a comprehensive analysis of the properties of compact stars, which will undoubtedly contribute to our understanding of these astrophysical phenomena.

The High Energy X-ray Probe (HEX-P): probing accretion onto stellar mass black holes

Accretion is a universal astrophysical process that plays a key role in cosmic history, from the epoch of reionization to galaxy and stellar formation and evolution. Accreting stellar-mass black holes in X-ray binaries are one of the best laboratories to study the accretion process and probe strong gravity—and most importantly, to measure the angular momentum, or spin, of black holes, and its role as a powering mechanism for relativistic astrophysical phenomena. Comprehensive characterization of the disk-corona system of accreting black holes, and their co-evolution, is fundamental to measurements of black hole spin. Here, we use simulated data to demonstrate how key unanswered questions in the study of accreting stellar-mass black holes will be addressed by the High Energy X-ray Probe (HEX-P). HEX-P is a probe-class mission concept that will combine high spatial resolution X-ray imaging and broad spectral coverage (0.2–80 keV) with a sensitivity superior to current facilities (including XMM-Newton and NuSTAR) to enable revolutionary new insights into a variety of important astrophysical problems. We illustrate the capability of HEX-P to: 1) measure the evolving structures of black hole binary accretion flows down to low (≲ 0.1%) Eddington-scaled luminosities via detailed X-ray reflection spectroscopy; 2) provide unprecedented spectral observations of the coronal plasma, probing its elusive geometry and energetics; 3) perform detailed broadband studies of stellar mass black holes in nearby galaxies, thus expanding the repertoire of sources we can use to study accretion physics and determine the fundamental nature of black holes; and 4) act as a complementary observatory to a range of future ground and space-based astronomical observatories, thus providing key spectral measurements of the multi-component emission from the inner accretion flows of black hole X-ray binaries.

Artificial neural networks for the wavelet analysis of Lane-Emden equations: exploration of astrophysical enigma

ABSTRACT The equations of Lane-Emden (LE) can be visualized in various phenomena of astrophysics, fluid mechanics, polymer science and material science, thus the main concern of the present study is to put a novel effort to resolve these equations by utilizing the artificial neural networking approach incorporation with Vieta-Lucas wavelets called as VLW-ANN method. This unique combination of neural networking and Vieta-Lucas wavelets has been prepared to reduce the computational challenges as well as to overcome the obstacles while dealing with singularity. Many examples of the LE variety are solved by this approach. The effectiveness, accuracy and simplicity of the VLW-ANN scheme are demonstrated by a comparative study between the VLW-ANN results and existing results. Additionally, the results are shown in tables and figures, which give a more favorable impression of the scheme’s dependability. VLW-ANN scheme will provide interesting results for other non-linear models.

Pulsation in TESS Objects of Interest

We report the discovery of three Transiting Exoplanet Survey Satellite Objects of Interest (TOI) with signatures of pulsation, observed in more than one sector. Our main goal is to explore how large is the variety of classical pulsators such as δ Sct, γ Dor, RR Lyrae and Cepheid among TOI pulsators. The analysis reveals two stars with signatures of δ Sct and one of γ Dor, out of a sample of 3901 TOIs with available light curves (LCs). To date, there is a very scarce number of known pulsating stars hosting planets. The present finding also emerges as an exciting laboratory for studying different astrophysical phenomena, including the effects of star–planet interaction on pulsation and timing detection of planetary companions. We have also identified 16 TOI stars with periodicities and LCs morphology compatible with different classical pulsating classes, but for most of them, the dominant frequency signals originate from contaminating sources.

Observation of rapid flux coalescence in merging field-reversed configurations

Rapid magnetic reconnection was experimentally observed to occur within a microsecond timescale, leading to the field-reversed configuration (FRC) comprising a single closed magnetic field structure. The compressibility of the plasma within the FRC played a crucial role in accelerating the coalescence process, making it considerably faster than the resistive process. A strong similarity between the observed experimental results and those of the coalescence of solar flare loops indicates that astrophysical phenomena and laboratory plasmas are governed by a common physics.

A study on unveiling the secrets of exoplanet hunting

Exoplanets are celestial bodies outside our solar system, orbiting stars other than our sun. They come in various sizes, compositions, and distances from their host stars. Scientists detect exoplanets by observing the dimming of a star's light as a planet passes in front of it (transit method), measuring the gravitational tug a planet exerts on its star (radial velocity method), or directly capturing their images. Studying exoplanets is a captivating area of astronomy that unveils our universe's vast array of planetary systems. Researchers delve into these distant worlds to explore their atmospheres, structures, and potential habitability, aiming to gather insights into the likelihood of life existing beyond our solar system. This paper addresses the challenges of distinguishing exoplanet signals from stellar activity, instrumental noise, and other astrophysical phenomena. It discusses the role of data-driven approaches, machine learning, and advanced statistical analyses in enhancing the reliability and accuracy of exoplanet detections after applying KNN.

Metallofullerenes as potential candidates for the explanation of astrophysical phenomena.

Detection of complex organic species in space has been one of the biggest challenges of the astrophysical community since the beginning of space exploration, with C60-fullerene representing one of the largest molecules so far detected. The presence of small metal-containing organic molecules, like MgNC or CaCN, in space, promoted the idea that C60 may also interact with metals and form metallofullerenes based on the fact that in certain circumstellar and interstellar environments, the ingredients for the formation of metallofullerenes, i.e., metal and fullerenes, are abundant. In this perspective, we summarized the current effort to explore the presence of metallofullerenes in space, which started soon after the discovery of fullerenes about 40 years ago. Several implications of astrophysical phenomena were briefly discussed and shown to be addressable as the possible consequence of metallofullerenes' presence. We highlighted the spectral fingerprints that might be followed to achieve the future detection of cosmic metallofullerenes from a combined effort of laboratory and quantum chemical calculations. These results are expected to gain great importance with the James Webb Space Telescope (JWST), whose capability of unprecedented high sensitivity and high spectral resolution in the far- to mid-infrared range could aid the unequivocal detection of metallofullerenes in space.

Detecting Fast Radio Bursts with Spectral Structure Using the Continuous Forward Algorithm

Detecting fast radio bursts (FRBs) with frequency-dependent intensity remains a challenge, as existing search algorithms do not account for the spectral shape, potentially leading to nondetections. We propose a novel detection statistic, which we call the Kalman detector, that improves the sensitivity of FRB signal detection by incorporating spectral shape information. The detection statistic is based on an optimal matched filter, marginalizing over all possible intensity functions, weighted by a random walk probability distribution, considering some decorrelation bandwidth. Our analysis of previously detected FRBs demonstrates that the Kalman score provides a comparable yet independent source of information for bursts with significant spectral structure, and the sensitivity improvement is of the order 0%–200% with a median improvement of 20%. We also applied the Kalman detector to existing data from FRB 20201124A and detected two new repeat bursts that were previously missed. Furthermore, we suggest a practical implementation for real-time surveys by employing a low significance soft-trigger from initial flux integration-based detection algorithms. The Kalman detector has the potential to significantly enhance FRB detection capabilities and enable new insights into the spectral properties of these enigmatic astrophysical phenomena.

Simple and general methods to identify terrestrial planets

This paper has introduced and examined some methods to generally distinguish whether an exoplanet is terrestrial, with the help of available data. These methods include analysing the exoplanet's orbital period, size, distance from the star, and density. By comparing these properties with the known characteristics of terrestrial planets, we can make an informed judgment about whether an exoplanet is terrestrial or not. Using the transit method, we can find an exoplanet and determine its orbital period and size. By applying Kepler's Third Law together with the radial velocity method, we can calculate the star-planet distance and the planet's density, respectively. However, it is important to note that these methods have their limitations and uncertainties. The transit method is limited by the probability of observing a transit due to randomly oriented planet systems, and the radial velocity method is only highly receptive to detecting massive planets in close proximity to the stars they orbit. Additionally, certain astrophysical phenomena can lead to false positives in exoplanet detection. Despite these limitations, the methods presented in this paper provide a foundation for determining the likelihood of an exoplanet being terrestrial. As technology advances and our understanding of exoplanets expands, we will continue to refine these methods and develop new ones, improving our ability to explore terrestrial planets and potentially discover life beyond our solar system.

X-ray detection of the most extreme star-forming galaxies at the cosmic noon via strong lensing

ABSTRACT Hyperluminous infrared galaxies (HyLIRGs) are the most extreme star-forming systems observed in the early Universe, and their properties still elude comprehensive understanding. We have undertaken a large XMM–Newton observing programme to probe the total accreting black hole population in three HyLIRGs at z = 2.12, 3.25, and 3.55, gravitationally lensed by foreground galaxies. Selected from the Planck All-Sky Survey to Analyse Gravitationally lensed Extreme Starbursts (PASSAGES), these HyLIRGs have apparent infrared luminosities >1014 L⊙. Our observations revealed X-ray emission in each of them. PJ1336+49 appears to be dominated by high-mass X-ray binaries (HMXBs). Remarkably, the luminosity of this non-AGN X-ray emission exceeds by a factor of about 3 the value obtained by calibration with local galaxies with much lower star formation rates. This enhanced X-ray emission most likely highlights the efficacy of dynamical HMXB production within compact clusters, which is an important mode of star formation in HyLIRGs. The remaining two (PJ0116−24 and PJ1053+60) morphologically and spectrally exhibit a compact X-ray component in addition to the extended non-AGN X-ray emission, indicating the presence of Active Galactic Nuclei (AGNs). The AGN appears to be centrally located in the reconstructed source plane images of PJ0116−24, which manifests its star-forming activity predominantly within an extended galactic disc. In contrast, the AGN in the field of PJ1053+60 is projected 60 kpc away from the extreme star-forming galaxy and could be ejected from it. These results underline the synergistic potential of deep X-ray observations with strong lensing for the study of high-energy astrophysical phenomena in HyLIRGs.

SAINT (Small Aperture Imaging Network Telescope)—A Wide-Field Telescope Complex for Detecting and Studying Optical Transients at Times from Milliseconds to Years

In this paper, we present a project of a multi-channel wide-field optical sky monitoring system with high temporal resolution—Small Aperture Imaging Network Telescope (SAINT)— mostly built from off-the-shelf components and aimed towards searching and studying optical transient phenomena on the shortest time scales. The instrument consists of twelve channels each containing 30 cm (F/1.5) GENON Max objectives mounted on separate ASA DDM100 mounts with pointing speeds up to 50 deg/s. Each channel is equipped with a 4128 × 4104 pixel Andor Balor sCMOS detector and a set of photometric griz filters and linear polarizers. At the heart of every channel is a custom-built reducer-collimator module allowing rapid switching of an effective focal length of the telescope—due to it the system is capable of operating in either wide-field survey or narrow-field follow-up modes. In the first case, the field of view of the instrument is 470 square degrees (39 sq.deg. for a single channel) and the detection limits (5σ level at 5500 Å) are 12.5, 16.5, 19, 21 with exposure times of 20 ms, 1 s, 30 s and 20 min, correspondingly. In the second, follow-up (e.g., upon detection of a transient of interest by either a real-time detection pipeline, or upon receiving an external trigger) regime, all telescopes are oriented towards the single target, and SAINT becomes an equivalent to a monolithic 1-meter telescope, with the field of view reduced to 11′ × 11′, and the exposure times decreased down to 0.6 ms (1684 frames per second). Different channels may then have different filters installed, thus allowing a detailed study—acquiring both color and polarization information—of a target object with the highest possible temporal resolution. The telescopes are located in two pavilions with sliding roofs and are controlled by a cluster of 25 computers that both govern their operation and acquire and store up to 800 terabytes of data every night, also performing its real-time processing using a dedicated fast image subtraction pipeline. Long-term storage of the data will require a petabyte class storage. The operation of SAINT will allow acquiring an unprecedented amount of data on various classes of astrophysical phenomena, from near-Earth to extragalactic ones, while its multi-channel design and the use of commercially available components allows easy expansion of its scale, and thus performance and detection capabilities.

Some Solution Methods for Lane-Emden Differential Equation

The Lane-Emden equations have been used to model some phenomena in astrophysics, such as mathematical physics and stellar structure theory. In addition, the Lane-Emden equation is a central equation in the theory of stellar structures. In this paper, we introduce the Lane-Emden differential equations. A special second order Lane-Emden differential equation is solved by He’s variational iteration, adomian decomposition method, homotopy analysis method, homotopy perturbation method, and finite difference method respectively. The results obtained are compared with each other and it is analyzed which method gives more reliable results and is more useful than the others.

Probing Schwarzschild-like black holes in metric-affine bumblebee gravity with accretion disk, deflection angle, greybody bounds, and neutrino propagation

In this paper, we investigate Schwarzschild-like black holes within the framework of metric-affine bumblebee gravity. We explore the implications of such a gravitational setup on various astrophysical phenomena, including the presence of an accretion disk, the deflection angle of light rays, the establishment of greybody bounds, and the propagation of neutrinos. The metric-affine bumblebee gravity theory offers a unique perspective on gravitational interactions by introducing a vector field that couples to spacetime curvature. We analyze the behavior of accretion disks around Schwarzschild-like black holes in this modified gravity scenario, considering the effects of the bumblebee field on the accretion process. Furthermore, we scrutinize the deflection angle of light rays as they traverse the gravitational field, highlighting potential deviations from standard predictions due to the underlying metric-affine structure. Investigating greybody bounds in this context sheds light on the thermal radiation emitted by black holes and how the modified gravity framework influences this phenomenon. Moreover, we explore neutrino propagation around Schwarzschild-like black holes within metric-affine bumblebee gravity, examining alterations in neutrino trajectories and interactions compared to conventional general relativity. By comprehensively probing these aspects, we aim to unravel the distinctive features and consequences of Schwarzschild-like black holes in the context of metric-affine bumblebee gravity, offering new insights into the nature of gravitational interactions and their observable signatures.

Matter accretion onto charged black holes in symmergent gravity

In astrophysics, accretion is a process where the black hole acquires matter. The gravitational energy is released as a result of the accretion and converted into radiation. Accretion onto dark compact objects, for example, neutron stars, white dwarfs, and black holes is a significant process in the astrophysical phenomenon. It is a fruitful way to examine the features of modified gravity theories by testing the analysis of their results related to dark compact objects. Here, we study the motion of a charged particle moving in near a charged symmergent black hole with Maxwell field. The symmergent gravity is a newly developed modified theory gravity within the framework of the vacuum energy VO, gravitational constant G, and quadratic curvature coefficient cO. The vacuum energy VO can be defined in terms of G and cO in the case where all the fields are degenerate in the form of mass. Further, two different choices of the parameter α provide us two different black hole spacetimes, like de Sitter for α<1 and anti-de Sitter for α>1. For this, we explore the accretion of perfect fluid onto the spherically symmetric charged symmergent black hole. Then, we get analytical results among the four-velocity and energy densities of the accreting matter. Further, we investigate it for well-known fluids flowing onto a charged symmergent black hole. Applying the Hamiltonian approach, we are able to explore the nature of accretion for these fluids such as ultra-stiff fluid, ultra-relativistic fluid, radiation fluid, and sub-relativistic fluid onto the source mass. For this study, we classified isothermal types of fluid in the context of equations of state. In addition, we introduced the application of polytropic test fluid associated with accretion disks. The accretion rate is analyzed near a charged symmergent black hole, which produced a typical behavior presented graphically by the significant parameters α and Q.

In situ cryogenic transmission electron microscopy observation on the formation of hydrogen-ordered hexagonal ices and its astrophysical implications

ABSTRACT Water ices play a critical role in various astrophysical phenomena and store information about the thermal history of icy grains. To understand this history, clarifying the formation conditions in astrophysical environments is critical. In addition to taking the form of amorphous ices, ice can take four crystalline forms: hexagonal ice I (ice Ih), cubic ice I (ice Ic) and hydrogen-ordered hexagonal ice (ice XIh) and cubic ice (ice XIc). The aim of this article is to study the conditions for phase transitions among these different crystalline ices. We found through cryogenic transmission electron microscopy observations that some polymorphs of ice XIh were formed by simple annealing of ice Ih at 120–150 K without any dopant or irradiation. We also investigated the formation conditions of ice Ih by vapour deposition and heating of ice Ic in protoplanetary discs. The transition kinetics from ice Ih to ice XIh suggested that ice XIh exists between the transition temperature from ice Ic to ice Ih and 150 K. From these results, we constructed a water-vapour flux–temperature–time diagram that clarifies the amorphous, Ic, Ih, XIc and XIh ice phases. We found that, under the conditions encountered in most protostars, hydrogen-ordered ices XIh and XIc can exist just outside the snow line and below 125 K, respectively. The infrared libration modes should enable these phases to be distinguished observationally. Because some of these phases are chiral, their presence could fundamentally affect the evolution of other homochiral organic molecules that develop on their surface.

Tidal disruption of white dwarfs in a modified gravity theory with SPH

Abstract Low energy imprints of modifications to general relativity are often found in pressure balance equations inside stars. These modifications are then amenable to tests via astrophysical phenomena, using observational effects in stellar astrophysics that crucially depend on such equations. One such effect is tidal disruption of stars in the vicinity of black holes. In this paper, using a numerical scheme modelled with smoothed particle hydrodynamics, we study real time tidal disruption of a class of white dwarfs by intermediate-mass black holes, in the low energy limit of a theory of modified gravity that alters the internal physics of white dwarfs, namely the Eddington inspired Born-Infeld theory. In this single parameter extension of general relativity, the mass-radius relation of white dwarfs as well as their tidal disruption radius depend on the modified gravity parameter, and these capture the effect of modifications to general relativity. Our numerical simulations incorporating these show that departure from general relativity in these scenarios might be observationally significant, and should therefore be contrasted with data. In particular, we study observationally relevant physical quantities, i.e., tidal kick velocity and trajectory deviation of the remnant core and fallback rates of the tidal debris in this theory and compare them to the Newtonian limit of general relativity. We also comment on the qualitative differences between the modified gravity theory and one with stellar rotation.

Novel Explosive and Super Fractional Nonlinear Schrödinger Structures

The fractional nonlinear Schrödinger equation solutions have been investigated via fraction space-time derivative sense. We applied the unified technique for this model to extract new structures of waves. The fractional property structures were obtained from the model in form of hyperbolic, soliton, shock, explosive, superperiodic, and trigonometric structures. It was found that increasing fractal factors produces a change in the phase and wave frequency of propagating nonlinear waves. The physical models that explain tidal energy generation are crucial to the development of contemporary green power systems. The parametric description for wave characteristics in this process is created by the solution of nonlinear equations. The obtained solutions are applicable in new communications, energy applications, fractional quantum modes, and in science and complex phenomena in astrophysics. Finally, the proposed technique can be implemented for further fractional physical models.

Existence and Uniqueness of Positive Solutions for Semipositone Lane-Emden Equations on the Half-Axis

Semipositone Lane–Emden type equations are considered on the half-axis. Such equations have been used in modelling several phenomena in astrophysics and mathematical physics and are often difficult to solve analytically. We provide sufficient conditions for the existence of a positive continuous solution and we describe its global behavior. Our approach is based on a perturbed operator technique and fixed point theorems. Some examples are presented to illustrate the main results.

Development of a data sonification toolkit and case study sonifying astrophysical phenomena for visually imparied individuals

Data is predominantly conveyed and analysed in a visual manner. Data sonification provides an alternative approach to data analysis, has a broader application (e.g., peripheral monitoring) and offers accessibility to an alternative cohort (e.g., the visually impaired). While there are countless data visualization tools available, producing data sonifications typically requires in-depth knowledge of audio software and/or computer programming. Research was undertaken into existing data sonification tools, and subsequently a Data Sonification Toolkit was developed using Abelton Live and Max for Live. The Toolkit was developed in particular as an alternative means of data analysis for use by multiple disciplines across a built environment firm. The key aims for the toolkit were that (1) it should be user-friendly and accessible to people without an in-depth knowledge of either Ableton or Max, (2) the sonifications produced be accurate and true representations of input data sets, and (3) the Toolkit should have the capability and flexibility to be expanded and customized by those with the expertise to do so. The Toolkit was used, in collaboration with astrophysicist Chris Harrison, to develop sonifications of astronomical phenomena for the visually impaired. These sonifications were presented at the British Science Festival in 2019.

Detecting Multiplanetary Systems with Gravitational Microlensing and the Roman Space Telescope

It is plausible that most of the Stars in the Milky Way Galaxy, like the Sun, consist of planetary systems, instead of a single planet. Out of the estimately discovered 3980 planet-hosting stars, about 860 of them are known to be multiplanetary systems (as of 2023 June). Gravitational microlensing, which is the magnification in the light of a source star, due to a single or several lenses, has proven to be one of the most useful astrophysical phenomena with many applications. Until now, many extrasolar planets (exoplanets) have been discovered through binary microlensing, where the lens system consists of a star with one planet. In this paper, we discuss and explore the detection of multiplanetary systems that host two exoplanets via microlensing. This is done through the analysis and modeling of possible triple-lens configurations (one star and two planets) of a microlensing event. Furthermore, we examine different magnifications and caustic areas of the second planet, by comparing the magnification maps of triple and binary models in different settings. We also discuss the possibility of detecting the corresponding light curves of such planetary systems with the future implementation of the Nancy Grace Roman (Roman) Space Telescope and its Galactic Time Domain survey.